This invention relates to electro-optic shutters employing a suspension of dipole rod-like particles oriented for light transmission or rejection by an electric field. The term electro-optic shutter is intended to include more generally electro-optic cells useful for variable density filters, light choppers, displays, controllable polarizers and the like. Electro-optic fluid shutters have found a place in the art and representative are various Marks U.S Pat. Nos. 3,848,964, 3,527,525, RE 28,211, 3,512,876, 3,341,274, 3,257,903. Often discussed in these references is the problem of response time: although the dipole particles respond rapidly to an applied field and are oriented to provide a transparent window, the opaquing of the window tends to be slow by comparison since the dipole rods must move into random orientations by Brownian motion. Several of the references, for example, U.S. Pat. No. 3,848,964, describe forced disorientation by multi-electrode structure in the cell to which voltage pulses are applied generating a transverse electric field to provide a uniform positive disorientation of the dipoles. A limitation of this approach is that the transmittance of the panel depends on the proportion of the area taken up by the electrode lines as compared to the space between the lines. If the lines are far apart, the applied voltage to the conductors must be high to attain the necessary transverse field strength to move the dipoles. As the lines are moved closer together, the transmittance decreases.
In the present invention, the transverse electric field in the fluid shutter is provided by optically transparent piezoelectric transformer elements. A relatively low voltage such as 100 volts can be used to energize the piezoelectric voltage step-up transformer which then provides a combination of transverse electric field and motion to rapidly reduce the longitudinal alignment of the dipoles and the second transmitter of the cell.